How do you measure normal knee flexion?

How to Chart Normal Knee Flexion

Standard Measurement Technique

Use a universal goniometer with the patient supine, measuring from the lateral aspect of the knee with the axis centered over the lateral femoral epicondyle, the stationary arm aligned with the femoral shaft toward the greater trochanter, and the moving arm aligned with the fibular shaft toward the lateral malleolus. 1

Patient Positioning

• Position the patient supine (lying flat) on the examination table with the head and heels fully supported 2
• Ensure the knee is not hanging over the end of the table 2
• For standard goniometric measurement, the knee should be positioned in slight flexion (10-30 degrees) when measuring maximum flexion range 2
• Hip positioning can affect measurements; maintain consistent positioning with approximately 10 degrees of hip flexion for reproducibility 2

Measurement Tools and Accuracy

Universal Goniometer (Recommended Standard)

• The universal goniometer demonstrates excellent intratester reliability (ICC = 0.99 for flexion, 0.98 for extension) and good intertester reliability (ICC = 0.90 for flexion, 0.86 for extension) 1
• Long-arm goniometers are more accurate than short-arm goniometers, with a minimum significant difference of 10° versus 14° 3
• The goniometer does not require estimation of the joint axis, making it practical for clinical use 4

Alternative Measurement Methods

• Smartphone goniometry applications (such as ROM© or Knee Goniometer App) show strong correlation with universal goniometers (Pearson's correlation > 0.93) and may have smaller measurement error (0.62° vs 1.56°) 5, 6
• Digital inclinometers are the most accurate method available with a minimum significant difference of only 6° 3
• Visual estimation should be avoided when accurate documentation is required, as it has poor accuracy with a 14° minimum significant difference 3

Documentation Standards

What to Record

• Document the specific angle measured in degrees 1
• Record both active and passive range of motion separately if both are assessed 1
• Note the measurement tool used (universal goniometer, smartphone app, etc.) 6
• Include patient position during measurement (supine, weight-bearing, etc.) 2

Normal Values Reference

• Normal knee flexion typically ranges from 0° extension to 135-140° flexion 5, 4
• Document any limitations or inability to achieve full flexion (e.g., "unable to flex knee to 90 degrees") 2

Clinical Pitfalls to Avoid

• Do not use visual estimation alone for documentation requiring precision, as reliability is poor (ICC = 0.82-0.83) compared to goniometry 1, 3
• Avoid inconsistent patient positioning between measurements, as body position significantly affects readings 2
• Do not use short-arm goniometers when accuracy is critical; they have the same poor accuracy as visual estimation 3
• Ensure the goniometer arms are properly aligned with bony landmarks rather than estimating the joint axis 4
• Allow adequate rest period before measurement (typically 10 minutes) to ensure consistent readings 2

Serial Measurement Considerations

• For tracking changes over time, use the same measurement tool and technique consistently 1
• The same examiner should perform serial measurements when possible to minimize measurement error (intratester reliability is higher than intertester reliability) 1
• Document any factors that may affect measurement reproducibility, such as pain, swelling, or patient cooperation 2